Positron Kinetics in Soft Condensed Matter

We outline a new kinetic theory for positrons in soft matter, which blends together cross sections for positrons scattering from single molecules, with the structure function of the medium as a whole. Numerical results are presented for positrons in liquid argon, where negative differential conductivity arises from both positron formation and the structure of the medium.

Figure 1

Positron impact cross sections in dilute gaseous Ar ${\sigma }_i$ (see 6 and references therein) and structure-modified elastic cross sections ${\Sigma }_0-{\Sigma }_l$ in liquid Ar at 85 K.

Figure 2

The mean energy and Ps-formation rates for positrons in liquid and dilute gaseous Ar at 85 K as a function of $E/n_0$. These results are compared with the dilute gas phase results using Monte Carlo simulation [6].

Figure 3

The flux and bulk drift velocity of positrons in liquid and dilute gaseous Ar at 85 K as a function $E/n_0$. These results are compared with the dilute gas phase results using Monte Carlo simulation [6].

Figure 4

A plot of the static structure factor moment $s_0-s_1$ as a function of energy. The dashed curves represent the critical lines for structure-induced NDC: $d\ln (s_0-s_1)/d\ln ϵ=1$.